Glycerol Upgrading over Zeolites by Batch-Reactor Liquid-Phase Oligomerization: Heterogeneous versus Homogeneous Reaction

摘要

Glycerol upgrading to diglycerols in the presence of basic (Na(+) or Cs(+)) ion-exchanged (FAU or BEA) zeolite catalysts was studied in a liquid-phose batch rector at 260 degrees C under normal pressure. Homogeneous NaHCO(3) and CsHCO(3) catalysts were studied for comparison. All the catalysts, including NaHCO(3) and CsHCO(3), displayed the some conversion-selectivity relationship. The selectivity to linear diglycerols decreased at higher conversions/reaction times owing to the consecutive formation of higher oligomers, with preferential further conversion of alpha,alpha'-diglycerol. The maximum yield of linear diglycerols was limited to about 30%. The activities of the zeolites followed the order X > Y > Beta, independent of the alkali ion present. Catalysis by the zeolites starts with an induction period attributed to a slow leaching of alkaline cations from the zeolite. Thereafter, the reaction is characterized by a progressive loss of the microporous structure of the zeolite and increasing overlap of heterogeneous and homogeneous catalysis, where, primarily, the activity depends on the cation content of the zeolite.